Update chart post install instructions to point to runtime-class-manager

The chart post install instructions currently instruct installing a runtime class. This instead should be done by the runtime class manager.

current output:

spin-operator 0.6.1 is now deployed!

Your release is named spin-operator.

To learn more about the release, try:

  $ helm --namespace spin-operator status spin-operator
  $ helm --namespace spin-operator get all spin-operator

Note: spin-operator requires a few additional resources to be present on the
Kubernetes cluster before it can run the first Spin application. If you haven't
already done so, please ensure the following:

1. Install the containerd-shim-spin SpinAppExecutor:

  $ kubectl apply -f https://github.com/spinframework/spin-operator/releases/download/v0.6.1/spin-operator.shim-executor.yaml

2. Install the wasmtime-spin-v2 RuntimeClass:

  $ kubectl apply -f https://github.com/spinframework/spin-operator/releases/download/v0.6.1/spin-operator.runtime-class.yaml

You are now ready to deploy your first Spin app!

For further details, see this chart's README:

  $ helm show readme oci://ghcr.io/spinframework/charts/spin-operator

Proposed output:

spin-operator 0.6.1 is now deployed!

Your release is named spin-operator.

To learn more about the release, try:

  $ helm --namespace spin-operator status spin-operator
  $ helm --namespace spin-operator get all spin-operator

Note: spin-operator requires a few additional resources to be present on the
Kubernetes cluster before it can run the first Spin application. If you haven't
already done so, to quickly get started using the containerd-spin-shim executor, please do the following:

1. Install the containerd-shim-spin SpinAppExecutor:

  $ kubectl apply -f https://github.com/spinframework/spin-operator/releases/download/v0.6.1/spin-operator.shim-executor.yaml

2. Install the runtime-class-manager:

  $ helm install runtime-class-manager  \
  --namespace runtime-class-manager \
  --create-namespace \
  --version 0.1.0 \
  oci://ghcr.io/spinframework/charts/runtime-class-manager

3. Create Shim resource for installing the containerd-shim-spin binary. See an example here: https://raw.githubusercontent.com/spinframework/runtime-class-manager/refs/heads/main/config/samples/test_shim_spin.yaml

4. Label all Nodes where the shim should be installed (and thus where Spin Apps may run)
 
  $ kubectl label node --all spin=true

You are now ready to deploy your first Spin app!

For further details, see this chart's README:

  $ helm show readme oci://ghcr.io/spinframework/charts/spin-operator

Inspect the Helm chart's post-install output and the chart README referenced in the issue. Update the instructions to use runtime-class-manager, including the Helm install, Shim resource, and node-label steps shown in the proposed output. Done means the generated notes no longer direct users to install the RuntimeClass directly.